-There's plenty of ink in each cartridge.
-I've tried shaking each cartridge.

It prints black-and-white and color documents in faint red lines that is too hard to see.
Nothing was amiss, it just started like this all of a sudden

Perform a test print and see if this works. If it doesn't print properly your printer cartridge could be damaged, do you refill the cartridges? Clean the contacts of the cartridge.